Comparison of two- and four-magnetometer methods of measuring ventilation.

Two computerized methods of measuring ventilation from four pairs magnetometers placed anteroposteriorly (AP) and laterally on the rib cage and abdomen were compared with a method that employs two pairs of magnetometers placed AP on the rib cage and abdomen. This comparison showed that the most accurate method of measuring ventilation employed four-magnetometer pairs and a model that assumes that the rib cage and abdomen may be approximated by elliptical cylinders. In 10 subjects of widely varying body habitus, this method predicted lung volume change accurately during quiet breathing (R greater than 0.98) and during vital capacity maneuvers (R greater than 0.97). With this technique, we have confirmed that the rib cage contributes the majority (74%) of the volume change in the upright position. Additionally, we have shown that this method is sufficiently accurate to be used as a method of monitoring ventilation under a wide variety of tidal volumes, postures, and exercise states.